THE GENETICS AND BREEDING POTENTIAL OF RBT12, A DOMINANT DWARFING GENE IN WHEAT

Rht12, a dominant dwarfing gene of wheat, was shown to be located distally on the long arm of chromosome 5A. Lack of recombination with the awn inhibitor B1 suggested that Rht12 is either tightly linked to this gene or is, in this material, a pleiotropic expression of the gene. Linkage to beta-Amy-A1 was also very tight, indicating that Rht12 is present on the of chromosome 5AL ancestrally translocated from 4AL. The close linkage to beta-Amy-A1 also suggests that Rht12 is not a homoeoallele of the commercially important GA-insensitive dwarfing genes. Analysis of near-isogenic lines in a number of genetic backgrounds showed that Rht12 reduces height without altering ear size and significantly increases spikelet fertility. However its successful utilization in breeding programmes will require careful selection since in some backgrounds the gene reduces grain numbers and grain size. In all backgrounds, Rht12 delayed ear emergence time by around 6 days. A delay of this magnitude could, in many environments, adversely affect yield if it is not neutralized by altering the balance of other genes determining ear emergence time.